In existing multi-panel sectional doors, struts or stiffening beams are added to provide strength to the door. The struts or stiffening beams are normally separate members that are fastened to the door after its installation. The struts may be as simple as wooden boards, such as, two-by-fours or more complex metallic members that have been shaped to maximize reinforcement, systems that tension the door to provide strength, or integral struts formed as part of a polymeric panel.
For example, one design available in the industry incorporates a stiffener having a horizontal body, an inner vertical mounting flange and an outer bowed flange, where the vertical mounting flange and bowed flanges have free edges and respective beads or curls formed thereon to stiffen the flanges providing strength to the door. In another design, a reinforcing strut has multiple arcuate sections that strengthen the strut and provide for its attachment to the door. Still another design incorporates unique track assemblies that work in conjunction with rollers and restraining members to place each section in tension.
As mentioned, many of these designs incorporate flanges or other members, such as feet, that allow for attachment of the strut to the door by fasteners. While these members enjoy the advantage of determining the amount of strengthening at the time of installation, they require additional time to install. Also, the necessary mechanical fasteners, such as, screws and clips add to the cost of the door. As a further disadvantage, while the struts provide a great amount of stiffness, they typically do not distribute the stiffness uniformly unless several struts are used and spaced uniformly across the door. To achieve this type of uniformity with existing designs, for example, by attaching multiple uniformly spaced struts to the door, the amount of reinforcement may become unnecessarily high for the strengthening requirements of the door. As will be appreciated, this adds unnecessary cost and weight to the door.
In still another design in the industry, the panel sections, themselves, are formed with areas of increased thickness at their ends to strengthen, in effect, by integrally forming a strut in the panel. In contrast to those designs where the strut is separately attached, the integrally formed strut may not be adjusted in terms of size or location in response to the individual strength requirements of the door after the door has been manufactured. This design, also, increases the amount of packaging for the door and space needed for storage and shipment.